Photo-oxidation of polymers facts for kids
Have you ever seen an old plastic toy or a garden chair that has become faded and crumbly after being left outside? This happens because of something called photo-oxidation. It's a process where materials, especially plastics, start to break down when they are exposed to sunlight and air over time.
Think of it like this: the sun's energy and the oxygen in the air team up to attack the surface of plastic. This attack causes the plastic to change, making it weaker and more likely to break. Photo-oxidation is a big reason why plastics wear out when they are left outdoors.
Contents
What is Photo-oxidation?
Photo-oxidation is a scientific term that describes how light and oxygen work together to break down materials. In the world of polymer chemistry, which is the study of large chain-like molecules called polymers, photo-oxidation is a major type of material breakdown. Polymers are the building blocks of plastics, rubber, and many other everyday items.
When sunlight hits a plastic object, its energy can cause chemical reactions with the oxygen in the air. These reactions damage the long chains of molecules that make up the plastic. It's like cutting a long string into many smaller pieces. This cutting of the molecular chains is called chain scission.
Why Does Plastic Become Brittle?
When the long polymer chains break into smaller pieces, the material loses its strength and flexibility. Imagine a strong rope made of many long strands. If you cut most of those strands, the rope becomes weak and can snap easily. The same thing happens with plastic. As the chains break, the plastic becomes more and more brittle, meaning it can crack or shatter instead of bending.
This breakdown can lead to mechanical failure, which simply means the object stops working as it should because it's too weak. For example, a plastic garden hose might crack, or a plastic car part might break off.
The Problem of Microplastics
When plastics break down due to photo-oxidation, they don't just disappear. Instead, they often break into tiny, tiny pieces called microplastics. These microplastics are a big concern for the environment because they can end up in our oceans, soil, and even the air we breathe. Animals can mistake them for food, and they can carry harmful chemicals.
How We Deal with Photo-oxidation
Scientists and engineers have developed ways to either speed up or slow down photo-oxidation, depending on what the plastic is used for.
Protecting Plastics from Sunlight
For plastics that need to last a long time, like window frames, pipes, or parts of cars, we want to stop photo-oxidation. Special chemicals called UV-polymer stabilizers are added to these plastics. These stabilizers act like a sunscreen for the plastic, absorbing or blocking the harmful UV rays from the sun. This helps the plastic stay strong and colorful for many years, sometimes even decades.
Making Plastics Break Down Faster
On the other hand, for single-use plastics, like some packaging or disposable bags, we might want them to break down more quickly after they are used. To do this, special additives can be mixed into the plastic. These additives are designed to make the plastic more sensitive to light and oxygen, speeding up the photo-oxidation process. This helps the plastic fragment into smaller pieces faster, which can be a step towards it disappearing from the environment, though it doesn't mean it fully disappears right away.
Colors and Their Role
Even the colors in plastics and fabrics can affect how they react to sunlight. Some pigments (which give color) and dyes can absorb UV energy. This can sometimes protect the material, but other times it can actually make the breakdown worse. In textiles, when fabrics break down from light, it's called phototendering.
See also
- Photodegradation
- Polymer degradation
- Stress corrosion cracking
